Apparatus for direct reduction of iron oxide compacts

ABSTRACT

Apparatus for the direct reduction of iron oxides in compact form by preheating iron oxide compacts and enveloping them in hot inert particulate solids at the top of a columnar reactor then passing the mixture downwardly through the reactor countercurrent to an upward flow of natural gas that is introduced into the reactor bottom. Contact of the natural gas and the compacts with the hot solids results in reformation of the natural gas by reaction with carbon dioxide and the production of hydrogen and carbon monoxide, which hydrogen and carbon monoxide reduce the iron oxide of the compacts. Hot gases from the reactor are passed upwardly through a preheater for incoming iron oxide pellets and are then cooled, cleaned, and a portion returned to the bottom of the reactor. The reduced heated compacts are separated from the inert solids at the bottom of the reactor and are passed countercurrent to the natural gas that is being conducted to the reactor to heat it prior to introduction of the gas into the reactor bottom.

United States Patent Anthes etal.

[54] APPARATUS FOR DIRECT REDUCTION OF IRON OXIDE COMPACTS Pn'maryExaminer-Gerald A. Dost Attorney-Parmelee, Utzler & Welsh [72]Inventors: John A. Anthes, Carnegie; Joseph Vlnaty,

Aliquippa, both of Pa. [57] ABSTRACT Assign: Corporation Pittsburgh,Apparatus for the direct reduction of iron oxides in compact [22] Filed:A9529 1970 form by preheating iron oxide compacts and enveloping them inhot inert particulate solids at the top of a columnar reactor PP ,002then passing the mixture downwardly through the reactor countercurrentto an upward flow of natural gas that is introduced into the reactorbottom. Contact of the natural gas 3.1825] ..266/l9, 262122794 and thecompacts with the hot Solids results in reformation of the natural gasby reaction with carbon dioxide and the [58] Field of Search ..75/33-37,

266/154 7 19 20 29 production of hydrogen and carbon monoxide, whichhydrogen and carbon monoxide reduce the iron oxide of the [56]References Cited compacts. Hot gases frorn thereactor are passedupwardly through a preheater for incoming iron oxide pellets and areUNITED STATES PATENTS then cooled, cleaned, and a portion returned tothe bottom of the reactor. The reduced heated compacts are separatedfrom 2,592,783 A Spgl'll h i t lid t th b tt f th reactor d are passed 31 2/1959 Plke countercurrent to the natural gas that is being conductedto $377,106 3/ 1959 Aspegl'en the reactor to heat it prior tointroduction of the gas into the 3,205,065 9/1965 Mayer et al reactorbottonh 3,375,098 3/l968 Marshall.... 3,375,099 3/1968 Marshall ..75/ 6Claims, 2 Drawing Figures IRON OXIDE COMPACTS PREHEAT camp/tars t J l IREMOVE m4 TE}? FORM MIXTURE r0 PARTICULATE I $04103 DTSTR/BUTE HEAT 3 li coup/ease CONTACT MIXTURE l REHEAT INERT WI Th PART/DULA TE GASEOU-SREDUCTANTS REMOVE SOL IDS t WA TE? WA T E I? I l SEPARATE i M IXTURE OFFPORTION OF INERT I l PORTION 0F STREAM PAHT/CULH 6A8 STREAM L ID5 l IREDUCED l COM/"ACTS ENE/DH STREAM 9 A U AL t WI TH N 5:13 NATURAL 04sCD01. REDUCED counters l l STA BLE #500050 COMPA 0T5 PART/CULATE SHEET 1UF 2 IRON OX/DE COMPA C 7' .5

PREHEA 7' COM/ACTS FOR/W MIXTURE 7'0 D/STR/BUTE HEAT CONTACT M/XTUHEREHEAT M/ERT WITH PART/CULATE CASEOUS REDUCTA/VTS SOLIDS l SEPARATEM/XTURE Ill/EFT I I PART/CUL/ITE I SOL/D5 REDUCED CDMPACTS COOL REDUCEDCOMPACTS STABLE REDUCED REMOVE WA TER WA COMP/P538 REMOVE WA TER W4 OFFRoRT/anl 0F 0F a 4s STREAM 64s STREAM E/l/R/Ch' STREAM NATURAL WI TH 6A5NATURAL 645 llVl/E/V roRs their A Nor/rays MAR ATENTEUJAMIBISTZ fi sum 2OF 2 Wafer JOSEPH. VL/l/AT) WW doo o Reduced Pml/els j m e l 9 P M Qlily M m x 0 5 3 n 2 2 m u fi z W V m M w.

their Affarneys APPARATUS Emit DIME-CT MEDKICTMEN 01F IIRQN OXIDECUWACTS BACKGRGUND OF THE llNVEN'l'llON 1. Field of the invention Thepresent process and apparatus provide for the direct reduction of ironoxide in compact form using natural gas to supply the necessary reducingagents, and is an improvement in the method and apparatus disclosed inthe application of George A. Snyder and the herein named Joseph Vlnaty,Ser. No. 753,983, filed Aug. 20, 1968 assigned to the same assignee asthe instant application, and now US. Pat. No. 3,585,023,issued.lune15,1971.

2. Prior Art Natural gas is an excellent source of reducing gases foruse in reducing iron oxide in that it is readily available, easilytransported, low cost, and usually very low in harmful impurities suchas sulfur which are found in coal or other solid reducing agents.Attempts have been made to use natural gas as a source of reducingagents in direct reduction processes for iron oxide, but the commercialdevelopment of these processes has made little progress. In processesheretofore developed where natural gas has been used on a once-throughbasis, with spent gas being discharged, a voluminous quantity of gas isnecessary in an inefficient process. While it has been proposed to usereaction products along with more natural gas such as the processdisclosed in US. Pat. No. 3,375,098, external heaters are needed toeffect reforming of the spent gases and, since these reforming reactionsare endothermic, high fuel costs result.

BRlEF SUMMARY OF THE INVENTION in accordance with the present invention,a process and apparatus are provided for the direct reduction of ironoxides in compact form by charging a mixture of compacts and a highlyheated inert particulate solid material into the top of a columnarreactor and progressing the mixture downwardly countercurrent to a flowof natural gas that is introduced into the bottom of the reactor, Thecompacts are enveloped in the hot inert solids which are at atemperature sufficient to heat the iron oxides in the compacts toreducing temperature and the iron oxide is reduced by hydrogen andcarbon monoxide resulting from the reforming of the natural gas byreaction with carbon dioxide which takes place as the natural gaspermeates the hot mixture of granular solids and compacts in thereactor. The heat required for this highly endothermic reforming processis supplied in the reactor itself by the highly heated inert particulatesolid material. Reduced compacts and inert solids are removed from thebottom of the reactor and the reduced compacts are separated and cooledby contact with a mixture of recycle reactor gas and natural gas beingconducted to the reactor. The gases from the top of the reactor arepassed through a preheater for iron oxide compacts that are to becharged to the reactor and are then cooled and compressed and returnedto the bottom of the reactor along with additional natural gas.

BRIEF DESCON OF THE DRAWINGS FIG. 1 schematically illustrates by flowdiagram the reduction process of the present invention; and

FIG. 2 schematically illustrates an apparatus for carrying out theprocess.

DETAILED DESCRIPTION The present invention provides for the directreduction of compacts or pellets of iron oxide. The iron oxide compactscan be green or fired pellets, that is, pellets which have not beenheat-hardened or hardened pellets can be used. The latter are moreeasily handled and less subject to breakage or attrition in the reducingprocess. The compacts are preheated and charged into the top of anenclosed environment where they are mixed with and enveloped in a massof hot inert particulate solids. The term intert" as used herein'definesa material which does not interfere with the reduction of the iron oxidecompacts or adversely affect the reforming of natural gas to producehydrogen and carbon monoxide in the en closed environment underconditions necessary for these reactions. Inert solids which have thedesired heat capacity and chemical stability include various silicates,burned dolomite, aluminum oxide and silicon carbide, quartz and the likewhich are of a granular nature so as to be gas pervious. The particlesize of the granular material may vary provided that the materialenables sufficient gas flow through the reactor, with particles in theorder of one-eighth to one-fourth of an inch preferred.

The granular material is heated outside the enclosed environment to atemperature in excess of that which is required for reduction of theiron oxide compacts, generally on the order of 1,800 to 2,500 F. Byheating the granular material outside the enclosed environment,conditions for complete combustion of the fuel used for heating thegranular material can be achieved and the combustion can be completelycar ried out to produce carbon dioxide and water without fear ofcontaminating the reducing environment or reactor with these combustionproducts.

The primary purpose of the hot granular material is to quickly heat the.compacts to a temperature at which the ore will be reduced and asecondary purpose is to continuously supply heat to the interior of thereactor to replace that which is utilized in the reforming of thenatural gas supplied to the reactor without burning gas and air in thereactor or applying heat to the outside of the reactor to heat theinterior thereof. in addition, the granular material provides agas-permeable cushioning and segregating medium for the compacts. Thecompacts are enveloped in the granular material and the mixture descendsthrough the enclosed environment. The granular material cushions thecompacts and prevents their breakage or attrition while maintainingindividual compacts separate from other compacts during reduction sothat the compacts, which might otherwise fuse together as the oxide isreduced to metal, will not agglomerate or fuse together. To providesufficient segregation of the compacts, the volume amount of inertgranular material should substantially exceed the volume of thecompacts, as something on the order of 5-10 parts by weight of granularmaterial for each part by weight of compacts in the mixture.

After passage of the mixture of compacts and granular material throughthe enclosed environment countercurrent to a reducing gas and reductionof the iron oxide in the compacts has been effected, the hot reducedcompacts are separated from the granular material. Following separation,the reduced compacts are cooled by contacting them with the gases thatare being conducted to the enclosed environment. This not only cools thecompacts to an extent that they are stable to the atmosphere upondischarge from the apparatus, but results in the preheating of the gasflowing to the reactor to a temperature in the range of 1,800 to 2,000E, at which temperature some of the reforming reactions are thenaccelerated when the hot natural gas and recycle gas are introduced intothe en closed environment and contact the still hotter granular solidswithin the environment.

The use of natural gas to provide the reducing agents for iron oxideeliminates contamination of the reduced product by ash or sulphur aswhen coal, coke, or char are used as a reducing agent. Although a smallamount of solid reductants may be present in the compacts, the majorreduction is achieved through the use of natural gas to supply thereducing agents in the present invention. The components generally foundin natural gas such as methane, ethane or other lower hydrocarbons arereformed in the enclosed environment by carbon dioxide which, as isknown, is produced during the reduction of iron oxides. The reduction isschematically illustrated by the equation:

The carbon dioxide produced during the reduction is then availablewithin the enclosed environment and at the elevated temperature torefonn the components of the natural gas such as methane, according tothe equation: %CH +%CO,-'%CO+-%H,

to produce additional carbon monoxide and hydrogen for reducing the ironoxide in the enveloped compacts. These reforming reactions are highlyendothermic but, because of the presence of the mass of hot inertsolids, the temperatures within the reactor are maintained sufficientlyhigh to provide a highly reducing condition. Thus, all heat for thepresent process is provided'by the hot inert material and preheatedgases. Since the solids have a .higher heat-retaining capacity thangases, the presence of the solids retains more heat in the reactor thanwould be retained if only compacts and gases were present in the reactorwith no inert material to serve as a heat exchange but otherwise inertmedium. The necessary throughput of natural gas is thus minimized. Thisminimization is possible because the gases serve principally as reducingagents and not as the sole source of heat within the reactor.

The hot gases from the enclosed environment are passed into a preheaterand contacted with the incoming iron oxide compacts immediately prior tothe introduction of thecompacts into the reactor, and following this,these gases are withdrawn from the compact preheater.

in the presentprocess, the amountof natural gas which must be introducedinto the reactor and passed countcrcurrent to the iron oxide compacts inthe enclosed environment can be as low as about two times thetheoretical amount required for reduction. The specific quantity for anyparticular case is determined by heat transfer considerations, being theamount required to cool the reduced pellets to a temperature where theycan safely be exposed to the atmosphere without reoxidizing and also theamount required to adequately preheat the incoming pellets prior todischarge of the gas from the reactor.

The ofi' gas which is withdrawn from the compact preheater, containsmainly carbon monoxide and hydrogen, with lesser amounts of carbondioxide, methane or other hydrocarbons, and water which, as seen fromthe first equation above, result from the reduction of the iron oxide.This now partially cooled-off gas is then further cooled to remove thewater of reduction by a spray cooler or other condensing means, and ispreferably then passed through a compressor where the ab solute pressureof the gas is increased so that additional water can be removed in anadditional condensing means.

Prior to the return of some of the gas to the enclosed environment asrecycle gas, the gas stream has a portion thereof bled from the streamto maintain the desired pressure in the system and fresh natural gas ismixed with the stream to replenish it. The replenished stream is thenpreheated as above explained by contact with hot reduced compacts andintroduced, in a preheated condition, into the enclosed environment. Ifdesired, the gas bled from the stream can be advantageously used forpart of the fuel in the combustion chamber for heating the inertparticulate solids necessary for the process.

FIG. 2 illustrates the apparatus of the invention in which the closedenvironment is provided by an elongated vertical reactor l. The reactor1 is refractory lined or otherwise protected against the hightemperatures of the process. Iron oxide compacts 2 are charged through aconduit 3, which contains a star wheel 4 or other means to minimize theescape of gases or the influx of air, into a preheater 5 at the top ofthe reactor where they are preheated by off gases from the reactor. Thehot granular material 6, which has been heated to a temperature on theorder of 2,400 F is charged from a duct 7 which contains a regulatingmeans 8 into the upper end of the reactor. Means 8 regulates the rate ofintroduction of the granular material into the reactor and also preventsloss of gases from the reactor through the duct. The compacts 2 and hotgranular material 6 are mixed in a distributing means such as a divideror vibrator 9 and a distribution ring 10, the distributing meansinterconnecting the preheater 5 and columnar reactor 1. The mixture ofhot granular material and compacts is charged into the reactor andpassed by gravity through the section 11 of the reactor where reductionof the compacts is achieved. After sufficient contact time in thereactor, detenninedby the height of the reactor and rate of removal ofmaterial from the bottom of the reactor, the reduced compacts areseparated, out of contact with air, from the granular material by aninclined grate or refractory screen 12 at the bottom of the reactor. Thegranular material passes through the screen 12 while the reducedcompacts are moved to a cooling chamber 13.

The granular material, after separation from the compacts, istransferred through a chute to the heating chamber of a conventionalairlift furnace. The furnace has a refractory lined tubelike column 15that has a closed bottom with a hot combustion gas inlet 16 connectingit to a combustion chamber 17. Chamber 17 has an air inlet 18 and fuelinlet line 19. A supply of hot combustion gases from the chamber 17heats the granular material and carries it up the column 15. At the topof the column 15, a chamber 20 is provided to maintain a supply of hotgranular material for introduction to the reactor. A hot gas dischargeline 21 is provided to carry oh the spent hot combustion gases. Some ofthe spent gas may be used in heat transfer devices such as heatexchanger 22 to which combustion air is fed from a source (not shown)through line 23 to be preheated in the heat exchanger and then isdelivered through line 18 to the combustion chamber 19. The spent gasesare then discharged through line 24. Natural gas or other fuel is fed tothe combustion chamber through line 19 for admixture with the air fromline 18. Makeup granular material may be provided for the airliftfurnace through line 25 as required.

The reduced compacts, after separation from the granular material, arecooled by contact with the incoming natural and recycled reducing gas ina cooling chamber 13 are are then discharged through a star wheel 26 orother air-excluding device to a storage area 27. If desired, the reducedcompacts can be fed directly to a conventional steelmaking device.

In the initial startup of the process, natural gas is introduced from asource (not shown) to the cooling chamber through line'28 and conduit29. The gas passes upwardly through the cooling chamber 13, then throughline 30, and is introduced into the reducing section 11 of the reactor.Following the reduction and reforming reactions within the enclosedenvironment ofthe reactor, the gas flows through the preheater 5 in heatexchange relation to the compacts therein and is exhausted through exit31. The exhausted gas flows through line 32 to a condenser 33. Thecondenser, which may be a spraytype device, removes some water from thegas and the gas then flows through line 34 to a compressor 35 and thecompressed gas then flows through line 36 to a further device 37 forremoving additional water which may be present in the gas, after whichit passes through line 38 to a valve 39. Valve 39 distributes a portionof a cleaned and dewatered gas through the line 29 for admixture withfresh natural gas from line 28 and return to the reactor. Anotherportion of this gas is can'ied through bleed line 40 to the fuel line 19of the airlift furnace.

There has been described a process and apparatus for the directreduction of iron oxide compacts using natural gas as the source of thereducing agents. A hot inert solid material is used to heat the compactsand reducing gases to reduction temperature and to heat the natural gasto refonning temperaa. an elongated reactor having an upper receivingend and a lower discharge end,

b. compact receiving means above the receiving end of the reactorarranged to deliver compacts directly into the upper end of the reactorand through which off gases 5 from the reactor flow in heat exchangerelation to the compacts therein,

c. means for continuously heating granular inert material to a reactiontemperature for the compacts and arranged to mix it with the compactsentering the upper end of the reactor to envelope the compacts in thehot granular material with the compacts predominately isolated from oneanother,

(1. means for removing reduced compacts and the inert granular materialat the lower end of the reactor and separating the reduced compacts fromthe inert material out of contact with air, I

e. means for withdrawing reactor gases from said compact receiving meansand passing the reactor gases in heat exchange relation through thereduced compacts so separated, and discharging them into the lower endof the reactor,

f. means for mixing natural gas with the reactor gases being dischargedinto the reactor, and

g. means for additionally heating the hot inert material afier 25 it hasbeen separated from the compacts and recycling it to the upper end ofthe reactor.

2. An apparatus for the continuous reduction of iron oxide compacts asdefined in claim 1 wherein means is provided for separating a portion ofthe reactor gases after their withdrawal from the compact receivingmeans and before natural gas is mixed with the reactor gases.

3. An apparatus for the continuous reduction of iron oxide compacts asdefined in claim 2 including means for utilizing reactor gases soseparated as fuel in said means for additionally heating the hot inertmaterial.

4. in an apparatus for reducing iron oxide compacts having a columnarreactor and means for charging compacts and hot inert solids into thetop portion of the reactor and removing reduced compacts and inertsolids from the bottom, the improvement comprising:

a. a compact preheater positioned above the columnar reactor includingmeans at its top portion for charging compacts to the preheater andmeans for exhausting gases from the preheater,

b. means interconnecting the preheater and the reactor for distributingcompacts from the preheater randomly within inert solids charged to thereactor,

c. said means for charging hot inert solids to the reactor comprising aduct terminating at said distribution means,

d. means for preventing escape of gases from the distributing means intosaid duct while permitting free upward flow of gases from the reactor tothe preheater, and

e. means at the lower region of the reactor for introducing reducinggases into the reactor for upward flow through the reactor, distributingmeans and preheater.

5. In an apparatus as defined in claim 4 the additional improvementcomprising a cooling vessel. adjacent the lower region of the reactor,arranged to receive reduced compacts from the bottom of the reactor,through which said reducing gas is conducted prior to introduction intothe lower region of the reactor.

6. in an apparatus as defined in claim 5, the additional improvementcomprising means for conducting at least a portion of the off gasesexhausted from said preheater to said cooling vessel for retum to saidreactor.

2. An apparatus for the continuous reduction of iron oxide compacts asdefined in claim 1 wherein means is provided for separating a portion ofthe reactor gases after their withdrawal from the compact receivingmeans and before natural gas is mixed with the reactor gases.
 3. Anapparatus for the continuous reduction of iron oxide compacts as definedin claim 2 including means for utilizing reactor gases so separated asfuel in said means for additionally heating the hot inert material. 4.In an apparatus for reducing iron oxide compacts having a columnarreactor and means for chaRging compacts and hot inert solids into thetop portion of the reactor and removing reduced compacts and inertsolids from the bottom, the improvement comprising: a. a compactpreheater positioned above the columnar reactor including means at itstop portion for charging compacts to the preheater and means forexhausting gases from the preheater, b. means interconnecting thepreheater and the reactor for distributing compacts from the preheaterrandomly within inert solids charged to the reactor, c. said means forcharging hot inert solids to the reactor comprising a duct terminatingat said distribution means, d. means for preventing escape of gases fromthe distributing means into said duct while permitting free upward flowof gases from the reactor to the preheater, and e. means at the lowerregion of the reactor for introducing reducing gases into the reactorfor upward flow through the reactor, distributing means and preheater.5. In an apparatus as defined in claim 4 the additional improvementcomprising a cooling vessel adjacent the lower region of the reactor,arranged to receive reduced compacts from the bottom of the reactor,through which said reducing gas is conducted prior to introduction intothe lower region of the reactor.
 6. In an apparatus as defined in claim5, the additional improvement comprising means for conducting at least aportion of the off gases exhausted from said preheater to said coolingvessel for return to said reactor.